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Asus F402C Replacement Battery C21-X402 7.4V 5100mAh

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From $107.99 USD $129.99
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Fits Asus F402C, F402CA, X402CA notebooks; replaces OEM part C21-X402 battery.
7.4V, 5100mAh Li-Polymer cell restores full charge cycles to aging F402C packs that no longer hold capacity.
Connector slides onto the motherboard contact pin set with a single locking tab on the right edge.
We bench-tested this cell on an F402C unit; BMS accepted the swap on first insertion with no fault codes.
After installation, run one full discharge to sleep mode then charge uninterrupted to 100% — this resets the BIOS battery learn cycle and clears inaccurate health warnings.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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By continuing with your purchase, you acknowledge and agree to the estimated 7–10 business day delivery timeframe.
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

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⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

7.4V

Amp

5100mAh

Asus F402C Series — 7.4V Li-Polymer Replacement Battery (C21-X402)

This is a 7.4V, 5100mAh Li-Polymer replacement battery for the Asus F402C notebook. It fits the F402C, F402CA-WX102H, X402CA-WX094D, X402CA-1D, and over 20 additional F402/X402CA variants. When the original C21-X402 cell degrades and no longer holds charge, this unit restores portable power to the machine.

  • F402 and X402CA platform fit: These models share the same battery bay dimensions, 7.4V power rail, and C21-X402 connector. The BMS handshake uses the same two-wire communication protocol across the entire F402/X402 series, so one cell covers the full range.
  • Bench tested on actual hardware: We ran this cell through full charge and load cycles on an F402CA unit. The BMS completed charge termination cleanly at 8.4V and held protection thresholds correctly under sustained CPU and display load.
  • Post-install calibration on the F402C: After fitting this battery, run one full discharge down to the BIOS hibernate cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.

BIOS reporting poor battery health immediately after fitting the C21-X402

The F402C BIOS reads health data from EEPROM registers written by the original factory cell. When a new cell is installed, those registers don't match the new chemistry profile, so the BIOS flags the battery as degraded or unknown. This is a firmware read issue, not a fault with the replacement cell. Running one full discharge-to-hibernate and uninterrupted recharge gives the fuel gauge IC enough data to rewrite accurate state-of-charge values. After two full cycles, the health warning clears on most F402CA units.

Laptop shuts down at 20–30% charge shown on the F402C

This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The OS shows remaining charge based on stale EEPROM data, so the shutdown hits before the displayed percentage reaches zero. Under full CPU load plus backlit display, the cell voltage drops faster than the uncalibrated gauge predicts, and the BIOS pulls the plug to protect the circuit. Run two complete discharge-to-hibernate cycles and the gauge recalibrates — shutdowns at false percentages stop once the IC maps the real voltage cliff, which on this cell sits at approximately 6.0V under load.

Compatible Models

F402C F402CA-WX102H X402CA-WX094D X402CA-1D X402CA-WX011H X402CA-WX011D X402CA-WX142H X402CA-WX005H X402CA-WX058H X402CA-1A X402CA-WX066H X402CA-WX016D X402CA-1C X402CA-WX090D X402CA-WX061H X402CA-WX076D X402CA-WX054 X402CA-WX063H X402CA-WX012D X402CA-WX013D X402CA-1B X402CA-WX010D X402ca X402c X402

Replaces Part Numbers

C21-X402

Technical Specifications

Voltage7.4V
Amp Hours5100mAh
Capacity5100mAh
Rate37.74Wh
Net Weight214g /7.55 oz
Gross Weight474g /16.72 oz
Approximate Weight474g /16.72 oz
Dimension 303.90 x 81.26 x 8.75mm

Product Highlights

  • Brand: Asus
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-Polymer
  • Battery Type: Li-Polymer
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Asus F402C shows the replacement battery as "0% available (plugged in, not charging)" — what's actually happening?

The fuel gauge IC on the F402C is reading EEPROM data from the old cell and can't reconcile it with the new chemistry profile, so it reports 0% or refuses to charge. Disconnect the AC adapter, let the system run on battery until it hibernates, then plug in and charge uninterrupted to 100%. That forces the gauge IC to rewrite its calibration baseline. After one full cycle the charge percentage and charging state display correctly.

Windows says this battery has a 32Wh capacity but the spec shows 37.74Wh — is the cell actually underperforming?

The Wh figure Windows reports is pulled from the EEPROM design capacity field, which reflects the original factory cell's rated value — not a live measurement of the new cell. The C21-X402 replacement cell carries its own EEPROM data that may differ from what the original firmware expected. This is a register mismatch, not a capacity defect. Run two full calibration cycles and the reported Wh figure will converge closer to the cell's actual rated 37.74Wh.

The F402CA charges fine but the battery percentage jumps around wildly — drops 15% in two minutes then climbs back up?

The fuel gauge IC needs several full discharge and charge cycles to build an accurate voltage-to-capacity map for the new cell. Until it has that data, state-of-charge estimates swing sharply, especially during load spikes from the CPU or display brightness changes. This is not a fault with the cell itself. Run three complete discharge-to-hibernate cycles with uninterrupted charges to 100% and the gauge stabilises — erratic jumps typically stop after the third cycle.

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